Northern Ireland police are casting a wider net in their efforts to prove that Sinn Fein leader Gerry Adams once commanded the outlawed Irish Republican Army and ordered the 1972 killing of a Belfast mother of 10, according to colleagues.

Details of an expanding trawl for evidence emerged Saturday as detectives spent a fourth day questioning Adams about the IRA's abduction and killing of Jean McConville 42 years ago - an investigation that has infuriated his IRA-linked party.

Adams, 65, had been scheduled to be charged or released by Friday night but a judge granted police a 48-hour extension of his detention.

Sinn Fein's deputy leader, Martin McGuinness, said he had been told by Adams' legal team that detectives were questioning him about his speeches, writings and appearances going back to the 1970s, when he was interned without trial as an IRA suspect.

Aides to Adams and McGuinness said Catholic west Belfast residents with IRA affiliations had been approached by police recently, asking them to make statements about their knowledge of Adams' IRA activities.

Adams has always maintained he was never an IRA member. According to every credible history of the modern Sinn Fein-IRA movement, he joined the outlawed group in 1966 and rose quickly through the ranks, becoming its Belfast commander in 1972.